Poly-phase AC/DC Active Power Converter Startup Control
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Solution Overview
Problem
Existing poly-phase AC/DC active power converters face challenges with uncontrolled startup currents and harmonic distortion due to varying frequency power sources, and they struggle to maintain unity power factor and low harmonic distortion, especially when using phase-locked loop synchronization methods.
Innovation Solution
A poly-phase AC/DC active power converter that reconfigures to operate in a voltage boost mode at startup to reduce inrush currents and uses real-time geometric calculations to determine the conduction angle, ensuring unity power factor and low harmonic distortion by controlling the H-bridge converter with a DSP controller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the converter starts up in normal AC/DC conversion mode, then the control structure can operate immediately, but uncontrolled inrush current spikes occur due to lack of voltage gain
Solution Approach 1:
The converter performs preliminary action by entering voltage boost mode before normal AC/DC conversion mode during startup. This preliminary operation charges the DC-link capacitor to establish the necessary voltage gain, preventing uncontrolled inrush current when normal mode begins. The boost mode operates as a preparatory stage that eliminates the harmful effect of startup current spikes.
2Adaptability or versatility
If transformer designs are used to handle varying frequency, then power conversion is achieved, but the system becomes large, heavy, and expensive with additional line reactors
Solution Approach 1:
The invention replaces the mechanical/physical transformer system with an all-electronic active power converter. Instead of using physical transformers and line reactors to handle frequency variation, the converter uses electronic control of the H-bridge switching and DSP-based frequency tracking to adapt to varying input frequencies. This substitution eliminates the need for heavy magnetic components while maintaining frequency adaptability.
3Ease of operation
If PLL-based line synchronization is used, then power factor control is achieved, but significant errors occur during transient conditions when frequency changes
Solution Approach 1:
The invention changes the fundamental parameter used for frequency and phase tracking from fixed PLL timer intervals to variable DSP-based geometric calculations. The controller dynamically adjusts the sampling and calculation parameters based on the actual input frequency, allowing accurate phase angle measurement during both steady-state and transient conditions. This parameter adaptation enables precise power factor control even when frequency changes rapidly.
4Device complexity
If the converter operates without voltage gain at startup, then the control structure can be simpler, but current control becomes unstable due to lack of forcing function
Solution Approach 1:
The converter establishes preliminary voltage gain through boost mode operation before initiating normal AC/DC conversion. This preliminary action creates the necessary voltage difference (forcing function) that enables stable current control in the subsequent normal mode. The temporary addition of boost circuitry operation does not significantly increase overall complexity while ensuring control loop stability during the critical startup phase.
Data Source
AI summary
A three-phase AC/DC active power converter provides an H-bridge that is controlled by a DSP (digital signal processing) controller that places the H-bridge in a voltage-boost mode of operation when voltage of a DC-link capacitor maintained by the H-bridge is near than the voltage input from a three-phase power source. The voltage difference between the boosted DC-link voltage and the three-phase power source voltage provides a voltage potential thereby giving the control loops a possible gain value. The gain value provides loop stability to thereby prevent an inrush of electrical current into the power converter upon startup. The converter also allows harmonic distortion to be modified through wave shaping of the normally pure sinus conduction signal.